The Yamaha V9958 is a Video Display Processor (VDP) used in MSX 80s home computers. More specifically, the MSX 2+, MSX turbo R and the "TIM" upgrade to the TI-99/4A.
The Yamaha V9958, also known as MSX-Video, is the successor of the Yamaha V9938. It was clearly conceived not to be a very major upgrade to its predecessor, which hampered its adoption. The main new features are three graphical YJK modes (with up to 19268 colours) and horizontal scrolling registers.
Read more about Yamaha V9958: Specifications, MSX-specific Terminology